The advantages of a rotating or swinging laser source to define a reference light plane receivable by a detector positioned on a grade pole have been long appreciated by land surveyers. Because a rotating laser beam can define a sharply delineated narrow plane of light at even substantial distances from the laser source, considerable effort has been expended by surveying authorities in developing detection apparatuses to locate such laser planes. Typically, the detection apparatuses utilize an upright grade pole carrying a photocell which is slidably mounted on the grade pole, permitting an operator to slide the photocell upwardly and downwardly until it intercepts the laser plane and perceptibly indicates the interception to the operator. The operator then determines the distance between the center of the laser plane and the base of the grade pole. This distance is hereafter referred to as the grade distance or grade of the particular point at which the grade pole is situated.
The laser beam detectors now available for use in surveying have a pointer or hairline which moves with the photocell along the grade pole's linear scale, and using the pointer, the operator must read and interpolate the scale to obtain the precise vertical positions of the upper and lower edges of the laser plane. The accurate reading and interpolating of fine scale divisions requires skill and experience, and even then the scale can easily be misread, introducing error into the calculation. Accurate reading of the scale becomes increasingly difficult when the grade pole is located in a shadowy or semi-dark location such as the often poorly lighted interior of a building under construction. In the event the detector must be moved to a location on the pole which is above the operator's eye level in order to intercept the laser beam, it is still more difficult for the operator to accurately read and interpolate the scale divisions. The same difficulty arises when the detector is moved to a location on the grade pole where the operator must kneel or bend over to read the scale divisions. These difficulties have been eliminated by the present invention.
Another shortcoming of the now available laser detection apparatuses for land surveying is that while they measure grade distance, none are able to measure the distance between the laser source and the grade pole, hereafter called the range distance or range. It is desirable that the surveyor be able to easily determine the range distance, and the present invention digitally displays this distance on command without any calculations being required of the operator.
Still another shortcoming of most available detection apparatuses is that they are ineffective in bright daylight due to sunlight masking the laser beam from the detector, which is typically a photocell. It would be desirable to provide a detector usable under any likely-to-be-encountered lighting conditions. The present invention provides such a detector.